A conventional I.S. glass container manufacturing machine comprises a series of sections arranged along side each other and operating out of phase with each other. Each section is equipped with a single parison transfer invert mechanism carrying one or more neck-rings. Taking single gob operation as an example, the machine cycle commences with the neck-ring in a reverted position and the parison mould closed around it. A charge or gob of glass enters the upper end of the parison mould and is blown or pressed into a parison shape with some glass being forced into the space between the neck-ring and a plunger to form a finish end portion of the final container. The parison mould then opens leaving the parison held by its finish end in the neck-ring. The invert mechanism then operates to carry the parison from the parison forming station and to invert it into the blow mould station where the blow mould closes around it. The neck-ring is then opened, dropping the parison into the blow mould where it is supported by a bead formed on the finish. The invert mechanism returns the neck-ring to the parison forming station and the parison mould closes around it ready for the next charge of glass. Meanwhile the parison hanging in the blow mould is reheating, that is to say the outer, cooler, skin of glass which gives it its shape retaining ability and thus allows it to be transferred without excessive distortion from the blank mould to the blow mould, receives heat from the hotter interior glass and softens. This allows the body of the parison to stretch under its own weight and its outer surface to achieve a condition at which the parison can be blown into a final container. If blowing takes place before adequate reheating has occurred, a defective container will be formed with an unsatisfactory glass distribution.
Various steps have been taken in recent years to attempt to increase the speed of the container forming process, including the introduction of axial mould cooling methods and the reduction of the wall thickness of the finished container. There are however two problems which are still encountered.
One problem is that of achieving a sufficient cooling of the finish end portion of a parison so that it is sufficiently strong to withstand the further processing steps without distortion. Such cooling is best achieved through an increase in neck-ring contact time, but in a conventional I.S. machine increase in such time also increases the cycle time of the section. In U.S. Pat. No. 5,547,485 a solution to this problem has been proposed by the use of two neck-ring mechanisms within the space available in a normal I.S. section. This arrangement allows one mechanism to remain in position with the parison supported in the neck-ring mechanism, the finish cooling while the remainder of the parison reheats and stretches, while the other neck-ring mechanism moves towards a blank station of the section for the forming of the next charge of glass into a parison. This arrangement not only provides an increased neck-ring contact time, but allows for better utilisation of the parison moulds, as the formation of the next charge of glass into a parison can begin sooner with the second neck-ring mechanism in place against the parison moulds while the previous parisons are still supported by the first neck-ring mechanism.
A second problem which arises when attempting to increase the speed of a section and to decrease the weight of the formed containers, is that the time which is allowed for reheating becomes a disproportionate part of the total cycle. For example, to manufacture very light containers a parison is required which is, proportionately, shorter than normal in relation to the final container. Such a parison requires a correspondingly longer time to reheat and stretch before it can be satisfactorily blown, and it is found that the speed of the section has to be reduced to allow the blow mould enough time to perform its functions of holding the parison to allow it to reheat and subsequently blowing and cooling the finally formed container.
It has been proposed to overcome this problem by the introduction of an intermediate station at which the parison could reheat before being transferred to the blow moulds for final forming. In U.S. Pat. No. 4,010,021 the parisons were formed in an upright condition and transferred horizontally to an intermediate station where a set of intermediate jaws closed around finish end portions of the parisons, allowing the neck-ring mechanism to release the parisons and return to the blank station for the formation of the next parisons. After reheating of the parisons had taken place, the intermediate jaws were moved horizontally, carrying the reheated parisons to the final forming station where they were released into the blow moulds for final forming. One feature of this machine was that the timing of the mechanisms in the parison forming stage was effectively decoupled from the timing of the mechanisms in the final forming stage, thus allowing the reheat time to be varied without requiring retiming of the mechanisms operating at these two stages.
However this mechanism suffered from some disadvantages. Firstly, the neck-ring contact time with the finish end portions of the parisons was necessarily short. Consequently there tended to be inadequate cooling of the finish end portions of the parisons, resulting in damage and distortion firstly when the parisons were transferred from the neck-ring mechanism to the intermediate jaws and again when the reheated parisons were transferred from the intermediate jaws to the blow moulds. Secondly, after reheating the parisons were very soft, and liable to rock or distort on movement of the intermediate jaws to carry the reheated parisons from the intermediate station to the final forming station. As a consequence damaged or unsatisfactory containers were frequently formed.
A further development of the machine described in U.S. Pat. No. 4,010,021 is described in U.S. Pat. No. 4,255,179. In this later machine, the parisons were made, as is conventional in an I.S. section, in an inverted position and transferred by a conventional invert mechanism to the intermediate jaws. However this machine suffered from the same disadvantages as the machine of U.S. Pat. No. 4,010,021.
A further attempt to solve the problem was the so-called R.I.S. machine, the principle of whose operation is described in U.S. Pat. No. 4,343,644. In a section of this machine, parisons are made in a conventional I.S. machine parison forming station, and are then inverted by a conventional neck-ring mechanism and received by a first of a pair of sets of blow moulds arranged on a turret. After transfer, the blow moulds are closed about the parison, and the neck-rings caused to release the parisons and to return to the parison forming station. The turret is then rotated to bring the first set of blow moulds into a final forming station, bringing the second set of blow moulds into position to receive the next set of parisons. It was intended that each set of parisons would reheat in the closed blow moulds and could then, at a suitable time later in the cycle, be blown into final containers. In practice it was found that the parisons enclosed by the blow moulds had reheated to such an extent that rotation of the turret would case distortion of the parisons within the blow moulds, even though, in general, sufficient reheating to enable the parisons to be satisfactorily blown had not occurred. Consequently it proved necessary to begin the blowing operation before the turret began its rotation thus restricting the time available for reheating unless the cycle time was undesirably increased.
It is one of the objects of the present invention to provide an improved method of manufacturing glass containers in a section of an I.S. machine.